Japanese Patent Laying-Open No. 58-139678 (Patent Document 1) is a prior art document that discloses a configuration of an impulse voltage generating device. In the impulse voltage generating device described in Patent Document 1, decrease in a discharging starting characteristic as caused by humidity is prevented by the following configuration: a discharging gap is provided between stages of capacitors arranged successively and connected to a DC power source in parallel; a discharging bulb in each discharging gap is accommodated in a sealed inner container; the inner container is accommodated in a sealed outer container; and an air flow path for temperature adjustment is formed between both the containers.